CVS commit: src/sys/kern

["Jaromir Dolecek" <jdolecek%netbsd.org@localhost>]

Module Name:    src
Committed By:   jdolecek
Date:           Sun Apr 12 08:51:41 UTC 2020

Modified Files:
        src/sys/kern: vfs_wapbl.c

Log Message:
fix race between wapbl_discard() and wapbl_biodone() on forced
unmount on shutdown with slow I/O device

wapbl_discard() needs to hold both wl_mtx and bufcache_lock while
manipulating wl_entries - the rw lock is not enough, because
wapbl_biodone() only takes wl_mtx while removing the finished entry
from list

wapbl_biodone() must take bufcache_lock before reading we->we_wapbl,
so it's blocked until wapbl_discard() finishes, and takes !wl path
appropriately

this is supposed to fix panic on shutdown:
[ 67549.6304123] forcefully unmounting / (/dev/wd0a)...
...
[ 67549.7272030] panic: mutex_vector_enter,510: uninitialized lock (lock=0xffffa722a4f4f5b0, from=ffffffff80a884fa)
...
[ 67549.7272030] wapbl_biodone() at netbsd:wapbl_biodone+0x4d
[ 67549.7272030] biointr() at netbsd:biointr+0x7d
[ 67549.7272030] softint_dispatch() at netbsd:softint_dispatch+0x12c
[ 67549.7272030] Xsoftintr() at netbsd:Xsoftintr+0x4f


To generate a diff of this commit:
cvs rdiff -u -r1.106 -r1.107 src/sys/kern/vfs_wapbl.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.